Embodiments of the present invention relate generally to superjunction devices, and more particularly, to superjunction devices that can support higher blocking voltages while maintaining simplicity of manufacturability.
Since the invention of superjunction devices by Dr. Xingbi Chen, as disclosed in U.S. Pat. No. 5,216,275, the contents of which are incorporated by reference herein, there have been many attempts to expand and improve on the superjunction effect of his invention. U.S. Pat. Nos. 6,410,958, 6,300,171 and 6,307,246 are examples of such efforts and are incorporated herein by reference.
Superjunction devices, including, but not limited to metal-oxide-semiconductor field-effect transistors (MOSFET), diodes, and insulated-gate bipolar transistors (IGBT), have been or will be employed in various applications such as automobile electrical systems, power supplies, and power management applications. For example, superjunction devices may specifically be employed in light emitting diode (LED) televisions, electric or hybrid cars, LED light bulbs, servers, tablets, uninterruptable power supplies (UPS), and the like. Such devices sustain high voltages in the off-state and yield low voltages and high saturation current densities in the on-state.
FIG. 1 is an enlarged partial cross-sectional view of a prior art trench-type superjunction device 110. A semiconductor substrate 112 supports on its first main surface 112a a semiconductor layer 116. A plurality of trenches 118 (two shown) are formed in a main surface 116a of the semiconductor layer 116 and extend into the substrate 112. The trenches 118 are filled with a semi-insulating or insulating material 119, and form in an active region a plurality of mesas, each of which has alternating n and p columns 120, 122. In this type of superjunction device 110, the semiconductor layer 116 has a thickness T of about 45 micrometers (μm), and supports a blocking voltage of up to about 650 Volts (V), and in some cases up to about 700 V. Other prior art structures, including non-trench superjunction devices, which are composed of up to seven epitaxially grown semiconductor layers, achieve similar blocking voltages.
FIG. 2 is an enlarged partial cross-sectional view of an attempt to improve the blocking voltage of a prior art trench-type superjunction device. The device 210 shown in FIG. 2 is similar to the device 110 of FIG. 1, with the exception that the thickness T of the semiconductor layer 216 is about 55 μm or greater. Blocking voltages higher than 700 V can be achieved by device 210, but there are significant drawbacks to this technique. For example, the trenches 218, which are typically formed by deep reactive ion etching (DRIE), are necessarily deeper in order to reach the substrate 212, and therefore require longer etching times, which increases the manufacturing expense. The deeper trenches 218 are also more difficult to refill. There is further a significant increase in the stress placed on the device 210, and the potential for warpage thereof is greatly enhanced.
It is therefore desirable to provide a superjunction device that permits an increase in the blocking voltage, but is easier to manufacture and avoids the drawbacks of the design shown in FIG. 2.